Is very difficult for an architecture student says which one is your favourite building. In my case i dont have one specific favourite buinding but i have different builnding that i like.
One of these building is the Coliseo located in Rome. Is one of my favourites specially for the history of the building and the intelligence of the romans people to build so huge building with less materials and technology that today.
The roman coliseo is an icon and emblem in the city today.

For another hand i like the sports specially soccer. For that i love the soccer stadiums. In the postmodern examples of stadiums The Allianz Arena in Munich by Herzog and de Meuron is my favourite. Inserted in the context, the builnding participate in the soccer show changing the colours of lights depending which team use the stadium. the stadium is covered but this membrane that change of colour.

The nest stadium of the same architects is another of my favourites buildings too.